With 21 moons and nine major rings, the periphery of Uranus is already crowded—and it's only getting worse. Thanks to the Hubble Space Telescope, scientists have learned that there are at least two more moons and two more rings orbiting "the Bull's-Eye Planet." The rings are removed from the previously known cluster and are thus called the "second ring system."

The significance of the discovery lies in the outermost ring, which shares its orbit with the new moon Mab. The ring is made up of lunar dust, and is replenished with fresh dust each time a meteoroid blasts into Mab. This process indicates a "youthful and dynamic system of rings and moons," according to scientists at the SETI Institute.

The Hubble data also revealed, somewhat surprisingly, that the orbits of Uranus' inner moons has changed significantly over the past 10 years, suggesting an unstable orbital environment.—Adam Raymond